1. Field of the Invention
The present invention relates generally to an improved bipolar electrode and, more particularly, but not by way of limitation, to an improved bipolar electrode having an anodic member and a cathodic member connected in a spaced apart relationship.
2. Brief Description of the Prior Art
In the past, many electrolytic cells have been proposed for use in a variety of applications. Various electrodes for use in electrolytic cell applications have also been proposed in the past.
One type of electrolytic cell included an anode electrode and a cathode electrode immersed in an electrolyte and an electrical power source connected to the anode electrode and the cathode electrode, the positive side of the power source being connected to the anode electrode and the negative side of the power source being connected to the cathode electrode. In this type of electrolytic cell, the electrode functioning as the anode and the electrode functioning as the cathode were generally referred to in the art as "monopolar" electrodes, i.e. each electrode functions as either an anode or a cathode during electrolysis.
Another type of electrolytic cell included an anode electrode and a cathode electrode and at least one electrode interposed between the anode and the cathode electrodes, each of the electrodes interposed between the anode and the cathode electrodes having an anodic member and a cathodic member and being referred to in the art as "bipolar" electrodes. The cathodic member and the anodic member of each bipolar electrode were mechanically connected, and the cathodic member of each of the bipolar electrodes was electrically in series with the anodic members prior and subsequent thereto, i.e. the current flowed through the electrolyte to the cathodic member of the bipolar electrode, through the bipolar electrode and from the anodic member of the bipolar electrode through the electrolyte to the next cathodic member of another bipolar electrode or to the cathodic member of the cathode electrode depending on the number of bipolar electrodes in the electrolytic cell.
In the past, electrodes constructed of a carbon material have been used in the construction of both monopolar electrodes and bipolar electrodes. In some instances, the anodic surfaces were constructed of a carbon material and the cathodic surfaces were constructed of a ferrous material, this type of construction tending to minimize contamination of the electrolyte which results from the electrolytic erosion of many non-carbon anodes.
Bipolar electrodes have been constructed of graphite and, in these instances, the graphite was continuously consumed during electrolysis as a result of oxidation of the graphite surfaces. As the graphite bipolar electrode was consumed, the voltage drop across the electrolytic cell was increased and the temperature of the electrolyte increased with the result being the establishment of an operating temperature range of approximately 25.degree. C. to approximately 70.degree. C. At the upper limit of this operating temperature range, the loss of graphite as a result of graphite oxidation was substantially increased and, in some instances, cooling coils were included in the electrolytic cell to cool the electrolyte in an attempt to maintain the electrolyte temperature at a reduced level (approximately 50.degree. C., for example).
The erosion of the carbon bipolar electrodes caused dimensional instability and resulted in a decreased current efficiency as the carbon bipolar electrode was operated over a period of time. Since the erosion of the carbon bipolar electrodes was not uniform, current density gradients were formed which caused further deleterious effects on the operational characteristics of the electrolytic cell.
In recent years, metal electrodes have been proposed to be operated as anodes in bipolar electrolytic cells, such bipolar electrodes also including a cathodic surface. For example, anodic surfaces of titanium have been proposed with cathodic surfaces bonded thereto and such bipolar electrodes have been proposed for use in chloride brines. A non-conductive film tends to form on exposed titanium anodic surfaces in chloride brines; however, this non-conductive film does not tend to develop on precious metals, such as platinum, for example, and platinum coated titanium anodic surfaces have been utilized in chlor-alkali electrolytic cell applications.
In the past, metal bipolar electrodes have been constructed of precious metal coated titanium sheets bonded to steel plates, the precious metal coated titanium sheets forming the anodic member and the steel plate forming the cathodic member. One problem encountered with such bi-metal bipolar electrodes was that the precious metal coated titanium sheet was deformed via the action of molecular hydrogen migrating through the cathodic member to the anodic member forming an expanded hydride with the titanium. This action resulted in a weakening of the structural integrity of the bond between the precious metal coated titanium sheet and the steel plate and, in many instances, resulted in a separation of the titanium-steel along the bonded surface.